Method and apparatus for fabricating high fin density heatsinks

ABSTRACT

A method of forming a high fin density heatsink from a plurality of fins each having a bottom portion of generally bell-bottom shape and a base unit of predetermined thickness having a plurality of grooves therein. The method comprises the steps of placing the plurality of fins loosely in respective ones of the grooves, and applying downward and horizontal pressure to the base unit intermediate respective ones of the fins for swaging the base unit so as to urge the fins downwardly into the respective ones of the grooves thereby creating a solid connection between the base unit and the fins with excellent thermal contact therebetween.

This is a divisional of application Ser. No. 08/ 213,075 filed on Mar.15, 1994, now U.S. Pat. No. 5,406,698.

FIELD OF THE INVENTION

This invention relates in general to the fabrication of heatsinks, andmore particularly to a method and apparatus for fabricating a high findensity heatsink from separately extruded fins and a base unit.

BACKGROUND OF THE INVENTION

It is known in the art to utilize heatsinks for dissipating heatgenerated by electronic circuits in modern devices. Such well knownheatsinks typically comprise a base unit to which the heat generatingelectronic devices are mounted, and a plurality of fins projecting fromthe base unit for dissipating the generated heat. It is an object ofthese heatsinks to maximize the surface area of the fins in order toprovide optimum heat transfer from the heat sink to the surroundingatmosphere. It is a further object of well known heatsinks to provide agood thermal contact between the base unit and the fins.

In order to achieve the latter mentioned object, according to knownprior art methods, heatsinks have been fabricated by metal extrusionthrough a die which is cut to the required shape specifications suchthat the base unit and fins are of integral construction. However, asdiscussed above, efficiency of operation of such heatsinks is regulatedby the surface area and amount of metal used versus the length of eachfin. The current design limit for prior art extrusion processes in termsof fin thickness to height, is 3:1 or less. Thus, in the event that, anextruded fin is excessively thin or excessively high, the pressure ofthe extruded metal has a tendency to destroy the die.

In an effort to overcome the problems of integral extruded heatsinks,and in an effort to provide increased fin density and overall height,certain prior art fabrication methods have used separate extrusion ofthe base unit and the fins, and subsequent assembly to form theheatsink. For example, U.S. Pat. No. 3,261,396 (Trunk) teaches a methodof securing corrugated metal fins to a base unit by means of epoxycement. Unfortunately, the epoxy gluing method disclosed in the Trunkpatent results in poor thermal conductivity between the base unit andrespective fins.

U.S. Pat. No. 3,216,496 (Katz) teaches separate fabrication of a bus baror base unit having, on its flat side, a plurality of slots forreceiving separately fabricated fins. The slots extend transversely thelength of the bar and are arranged so as to hold the fins insubstantially parallel relationship. The fins themselves arestrip-shaped and preferably of width equal to that of the bus bar. Thefins are joined to the bus bar by means of inserting the fins into theplurality of slots and then swaging the material between adjoining slotsinto intimate contact with the fins by means of a hydraulic pressoperating through a knife-edged tool. Unfortunately, the method taughtby Katz applies pressure only to the narrow line contacted by theknife-edged tool. This results in the material of the bus bar beingpushed to the side of the respective fins which creates an upwardpressure tending to lift the fins upwardly from the grooves, therebyleaving an air space at the bottom of the grooves in the bus bar, whichallows for air and moisture to enter resulting in corrosion and reducingthe thermal contact between the base unit and fins.

Various other patents disclose methods of joining fins to a base unit.For example, U.S. Pat. Nos. 3,312,277 (Chitouras) and 3,280,907(Hoffman) teach the use of dovetail connections for overcoming extrusiondifficulties in fabricating a heat dissipating device with the fins veryclose together. Additional patents of interest are as follows: U.S. Pat.Nos. 941,375 (Loud et al); 2,639,119 (Greenwald); 2,944,326 (Stradthauset al); 3,077,928 (Nihlen et al); and 4,733,453 (Jacoby). However, noneof the above references teach effective means for overcoming the probleminherent in the Katz fabrication method by which the material of thebase unit is pushed upwardly between respective ones of the fins therebycausing the fins to lift upwardly from the grooves.

SUMMARY OF THE INVENTION

According to the present invention, an apparatus and method is providedfor fabricating a high fin density heatsink by means of a plurality ofrollers for applying pressure on opposite sides of the fin for providingdownward and inward swaging against a dovetail joint. In particular, acombination of dovetail fin base and groove is provided with theapplication of rolling pressure on opposite sides of each fin resultingin vertical and lateral pressure of the base unit material tending topush the fin toward the bottom of the groove in the base. The secureconnection between the fins and the base results in good thermal contacttherebetween and prevents air and moisture from entering the groovesthereby preventing corrosion and allowing the heatsink to be anodized.

One consequence of swaging is that the vertical pressure has a tendencyto warp the base unit upwardly in the middle as a result of displacementof material along the top portion of the base unit during theapplication of vertical pressure. Therefore, in accordance with afurther aspect of the invention, an apparatus is provided comprising afurther plurality of rollers for de-warping the base unit.

Various additional aspects of the invention are as follows:

An apparatus for swaging a base unit of predetermined thickness andhaving a plurality of grooves therein for receiving respectivebell-bottom shaped fins to form a high fin density heatsink, saidapparatus comprising: a) a planar work surface; b) an axle mountedparallel to said planar work surface; c) a plurality of disks mountedfor rotation about said axle and spaced apart a sufficient distance toallow respective ones of said fins to pass therebetween; d) means foradjusting the height of said axle to provide a clearance between thecircumference of said disks and said planar work surface which is lessthan said predetermined thickness of said base unit, such that uponadvancing said base unit through said clearance respective ones of saiddisks apply downward and horizontal pressure to said base unitintermediate respective ones of said fins for swaging said base unit soas to urge said fins downwardly into respective ones of said groovesthereby creating a secure connection between said base unit and saidfins with good thermal contact therebetween.

A de-warping apparatus for straightening a plate which is bent such thata centre portion thereof is higher than outer porions thereof,comprising:

a) a plurality of rollers forming a support surface, centre most ones ofsaid rollers being mounted lower than outer most ones of said rollers;

b) an axle mounted above said rollers;

c) a plurality of disks mounted for rotation about said axle, centremost ones of said disks having larger radius than outer most ones ofsaid disks; and

d) means for advancing said plate between said rollers and disks,whereby a greater downward force is applied to the centre portion ofsaid plate than to said outer portions for de-warping said plate.

A method of forming a high fin density heatsink from a plurality of finseach having a bottom portion of generally bell-bottom shape and a baseunit of predetermined thickness having a plurality of grooves thereincomprising the steps of: a) placing said plurality of fins loosely inrespective ones of said grooves; and b) applying downward and horizontalpressure to said base unit intermediate respective ones of said fins forswaging said base unit so as to urge said fins downwardly into saidrespective ones of said grooves thereby creating a secure connectionbetween said base unit and said fins with good thermal contacttherebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of the preferred embodiments is provided belowwith reference to the following drawings, in which:

FIG. 1 is a perspective view of a heatsink manufactured in accordancewith the principles of the present invention;

FIG. 2 is a partially broken elevation view of the heatsink of FIG. 1following a swaging operation according to the present invention,showing a dovetail connection of base unit having grooves for receivingbell-bottom shaped fins;

FIG. 3 is a perspective view of an apparatus for swaging the base unitand fins to form the heatsink of FIG. 1;

FIG. 4 is a detail elevation view showing the positioning of a pluralityof rollers of the apparatus of FIG. 3 relative to the base unit andrespective fins in accordance with the preferred embodiment;

FIG. 5 is a similar view to FIG. 4 after swaging, wherein the rollersare omitted for clarity;

FIG. 6 shows an apparatus for aligning the fins prior to swaging, inaccordance with the preferred embodiment;

FIG. 7 is a perspective view showing mounting of the rollers on an axle;

FIG. 8 shows a portion of the apparatus of FIG. 3 for securing the baseunit prior to swaging;

FIG. 9 is a cross-sectional side view of the apparatus of FIG. 3 showingmeans for adjusting the axle height and details of the axle supportconstruction;

FIGS. 10, 11 and 12 are cross-sectional side views similar to FIG. 9which, in combination, show the passage of a base unit and fins throughthe apparatus of FIG. 3;

FIG. 13 is a perspective view showing a saw for trimming end portions ofthe fins which extend beyond the sides of the base unit after swaging;

FIG. 14 is a perspective view of an apparatus for de-warping the baseunit after swaging, in accordance with another aspect of the presentinvention;

FIG. 15 is a front view of the warped base unit subsequent to swagingbut prior to de-warping in accordance with the apparatus of FIG. 14;

FIG. 16 is a side view of the apparatus of FIG. 14;

FIGS. 17A, 17B, 17C and 17D show the various stages of warping andde-warping of the base unit as a result of the apparatuses of FIGS. 3and 14; and

FIG. 18 is a front view, partially in section, of the apparatus of FIG.14.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIG. 1, a heatsink is shown which has been fabricatedin accordance with the prior art. In this prior art heatsink a base unitB and a plurality of fins F projecting perpendicularly therefrom, areextruded as an integral unit using well known extrusion techniques andapparatus. However, as discussed above, such prior art extrusiontechniques are incapable of producing high fin density heatsinks.

Turning to FIG. 2, a heatsink is shown which has been fabricated usingthe apparatus and method of the present invention. The inventiveheatsink comprises a base 1 and a plurality of fins 3 which are swagedinto respective parallel grooves in the top surface of the base unit 1,as discussed in greater detail below. In the illustrated embodiment, thefins 3 are shown as having a generally serpentine profile for increasingthe heat dissipating surface area. However, the fins 3 may be made flatfor certain applications.

Turning momentarily to FIG. 4, the base unit 1 is shown in greaterdetail comprising a plurality of parallel generally rectangular grooves5, each of the grooves 5 incorporating rounded corners at a lowerportion thereof. It has been found that extrusions of the base portion 1in accordance with the design of FIGS. 2 and 4 is both simple andinexpensive. The fin 3 is shown with reference to FIG. 4 having aflanged bell-bottom lower portion. Thus, in accordance with the methodof the present invention, the plurality of fins 3 and base unit 1 areseparately extruded, and thereafter combined by inserting respectiveones of the fins 3 into the grooves and thereafter crimping or swagingthe fins 3 into the grooves for forming a dovetail connection by virtueof the respective flange portions, as discussed in greater detail below.

Turning to FIG. 3, in combination with FIGS. 4 and 5, the apparatusaccording to the present invention is shown for fabricating high findensity heatsinks, comprising a plurality of disks 7 mounted to an axle9. The axle 9 is mounted for rotation in a pair of adjustable heightmounting blocks 10. The disks are spaced apart a predetermined distanceequivalent to the distance between successive ones of the plurality ofgrooves 5. The clearance between the lower most portion of thecircumference of the disks 7 and the top of the working surface 11 (FIG.8) is adjusted to be slightly less than the thickness of the base unit1.

Preferably, each of the disks 7 has a width approximately equal to butno greater than the distance between successive ones of the plurality ofgrooves 5 minus the width of each of the fins 3.

With reference to FIG. 9, the working surface 11 which supports the baseunit 1 while it passes beneath the disks 7 is, in turn, supported by aroller 16 mounted to a second axle 18 which is also mounted in blocks10.

The height of the axle 9, and hence the clearance between the disks 7and working surface 11, may be adjusted by turning the handle 20 (FIG.3), which is connected to a rod 22 having a pair of geared wheels 24(only one such wheel being shown in FIGS. 3 and 9). The wheels 24 engagerespective cooperatively shaped wheels 26 each mounted to a further rod28 (only one such wheel and rod being shown in FIGS. 3 and 9).

Each rod 28 has, at an end opposite to the geared wheel 26, a threadedportion 29 (FIG. 3) which engages a gear wheel 30 of a threaded boltmember 32. Upon turning the handle 20, the rod 22 rotates, causing rods28 to rotate as a result of interaction between geared wheels 24 and 26.This, in turn, causes the gear 30 and threaded bolt 32 to rotate withinmounting block 20. The axle 9 is housed within a riser block 34 whichhas internal threads for receiving the threaded bolt 32. Thus, inresponse to rotation of the threaded bolt 32, the riser block 34 may beraised or lowered. According to the preferred embodiment, one rotationof handle 20 results in a axle height adjustment of approximately of2.5×10⁻³ inches.

Also shown in FIG. 9 is a pair of pneumatically controlled rollers 36and 28 which are adapted to rest on top of the fins 3 as they passthrough disks 7. The rollers 36 are required to securely hold down thefins 3 in the grooves 5 before pressure is applied during swaging. Therollers 38 are required to prevent the fins 3 from rolling upwardly andaround the disks 7 after swaging.

In operation, the fins are loosely placed in the grooves 5 of baseunit 1. The fins 3 are then aligned relative to the spaces betweenrespective disks 7 by means of the alignment tool 12 shown in FIG. 6.This tool comprises a plurality of teeth 14 spaced at equivalentintervals to the disks 7. In FIG. 6, the non-aligned positions of thefins 3 are shown in phantom.

The loosely assembled unit is then advanced into the apparatus of FIG. 3by means of a pneumatic drive 16, such that respective ones of the fins3 pass between respective disks 7, as shown in FIG. 4. As the looselyassembled unit is advanced in the direction of arrow A in FIGS. 10, 11and 12, the disks rotate in the direction of arrow B and the roller 16rotates in the direction of arrow C, such that the lower mostcircumference portions of the disks 7 apply pressure to the regions ofbase unit 1 intermediate respective ones of the fins 3 for swaging themetal material in these regions to thereby crimp the fins 3 firmly inplace. The pressure provided by the apparatus of FIG. 3 on block 1 maybe adjusted by careful selection of the height of the axle 9.

The base unit 1 is held in place on working surface 11 by a pair ofpositioning bars 40 and 42 which are shown in detail with reference toFIG. 8. A pair of toothed side retention members 44 and 46 projectupwardly from the working surface 11, and are adapted to receivecooperatively shaped toothed end portions of the positioning bars 40 and42. Thus, the base unit 1, with fins 3 is held firmly in place on theworking surface 11 while the fins 3 are swaged into the base unit 1under pressure of disks 7. Turning to FIG. 7, each of the disks is showncomprising a raised circular hub portion 50 of predetermined thicknessagainst which an adjacent one of the plurality of disks rests. Thepredetermined thickness of the raised circular hub portion defines thedistance between respective ones of the disks 7. Each raised circularhub 50 has a keyway in the form of a rectangular slot 52 therein forreceiving a cooperatively shaped rectangular key 54 projecting from theaxle 9, in order to mount the disks 7 for rotation in conjunction withaxle 9.

The dovetail connection between the groove 5 and bell-bottom shaped fin3 of the present invention, in conjunction with the use of disk 7applying pressure vertically downward on base unit 1, results in thefins 3 being pushed downwardly by the displaced base unit material(shown in phantom with reference to FIG. 5), and into tight engagementwith the corresponding grooves 5.

As a result of the swaging operation according to the present invention,the fins 3 often become displaced laterally with reference to the baseunit 1. Therefore, according to the present invention, as shown in FIG.13, the heatsink is inverted and secured in a mounting device 60 and arotary blade 62 is used to cut through the excess portions of the fins 3for trimming such access portions off of the heatsink, in a straightforward manner.

Turning now to FIG. 14, the apparatus for de-warping the base unit i isshown comprising a plurality of pairs of disks 70 mounted to axle 72which, in turn, is housed in an axle block 74. The height of axle block74, and hence also of axle 72, is adjustable by means of threaded bolts71.

As the heat sink passes beneath and between rollers 70, the base unit 1is supported from beneath by a plurality of sub-rollers (shown inphantom with reference numeral 76 in FIGS. 14 and 16). The diameter ofthe outer two disk pairs 78 is made less than the diameter of the innertwo disk pairs 80 so that with base unit 1 supported on rollers 76, theinner disk pairs 80 exert a greater force on the center portion of thewarped base 1 than outer disk pairs 78 for flattening the warped baseunit 1 from the position shown in solid lines to the flattened shapeshown in phantom with reference to FIG. 15.

Turning briefly to FIG. 16, the axle block 74 is shown supported frombeneath by a pair of coil springs 92. As discussed above, the threadedbolt 71 controls the height of axle block 74 relative to the roller 76.More particularly, the bolt 71 is threaded into an internal threadedhole 90 and a portion of the bolt 71 contacts an upper portion of theaxle block 74 for applying equal and opposite pressure to the coilsprings 92.

Turning briefly to FIGS. 17A-17D, the various warped and de-warpedshapes of the base unit 1 are shown schematically. With reference toFIG. 17A, the base unit 1 shown in its initial flat configuration. InFIG. 17B, the base unit 1 is shown warped upwardly in the center as aresult of the swaging operation discussed in greater detail above withreference to FIG. 3. In FIG. 17C, the shape of base unit 1 isillustrated schematically to show the pressure of disk 70 on the topsurface thereof as the heat sink passes through the de-warping apparatusof FIG. 14. FIG. 17D shows the base unit 1 after de-warping, which issimilar to the initial flat shape of the base unit 1.

Turning now to FIG. 18, the rollers 76 discussed above with reference toFIG. 14 are shown in detail comprising a series of interconnectedsub-rollers 82 positioned so as to provide a constant clearance Dbetween respective ones of the pairs of disks 78 and 80 and theassociated sub-rollers 82, for effecting the de-warping discussed abovein connection with FIG. 17C. Thus, as shown in FIGS. 17C and 18, thebase unit 1 is flexed downwardly in the middle relative to the outeredges of the base unit 1, for de-warping the base unit.

In summary, the method and apparatus of the present invention result inlow cost fabrication of high fin ratio heatsinks, (eg. 6:1, 8:1, 10:1and greater). The heatsinks are characterized by high thermal contactbetween the base unit and fins with no moisture or air therebetween,thus preventing corrosion and permitting the part to be anodized.

Other modifications and variations of the invention are possible withinthe sphere and scope of the claims appended hereto.

I claim:
 1. A de-warping apparatus for straightening a warped heat sink,said heat sink comprising a plurality of fins extending perpendicular toa base plate, said base plate being bent such that a centre portionthereof is higher than outer portions thereof, comprisinga) a pluralityof rollers forming a support surface, centre most ones of said rollersbeing mounted lower than outer most ones of said rollers; b) an axlemounted above said rollers; c) a plurality of disks mounted for rotationabout said axle, said disks being spaced apart to allow said pluralityof fins to pass there between, and being of sufficient radius to allowclearance for said plurality of disks between respective circumferencesof said disks and said axle centre most ones of said disks having largerradius than outer most ones of said disks so as to provide a constantclearance between respective pairs of said disks and adjacent rollers;and d) means for advancing said plate between said rollers and disks,whereby a greater downward force is applied to the centre portion ofsaid plate than to said outer portions for de-warping said plate.